The invention relates to an improved process for preparing block copolymers containing polymerized lactone segments and to block copolymers containing polymerized lactone segments.
Lactone incorporation into polymer material can result in many improved performance benefits. Among these are improved impact resistance, improved optical properties, improved stress crack resistance. enchanced polymer processability, improved mold releasability, and improved carbon black and pigments dispersion. These benefits, coupled with the wide range of materials with which polymerized lactone-containing polymer is compatible, open up numerous new applcations which could not be filled by materials not having polymerized lactone segments therein.
The prior art has attempted anionic polymerization as a means for providing a polymerized lactone-containing polymeric material. The anionic ring-opening polymerization of lactones which involves acyloxygen cleavage with subsequent propagation through alkoxide anion also provides for the possibility of block polymerizing lactone molecules with other monomers or polymer segments. For example, the alkyl lithium-initiated polystyryl and polydienyl anions, or their corresponding oxyl-terminated anions, have been employed as macroactivators to cross-initiate lactone, such as caprolactone, polymerization. However, it has proved very difficult to channel the esterification reactions under the basic environment into the desired mode of selectivity to the exclusion of unzipping and scrambling transesterifications as the side reactions compete with polyester formation. The depolyesterification due to intramolecular transesterification, e.g., unzipping or backbiting phenomena produces cyclic ester oligomer contamination. Intermolecular transesterification (ester scrambling) generally results in uncontrolled molecular weight and broad molecular weight distribution.
A new approach to cope with the ester exchange side-reactions would be desirable.